This grant describes studies that are intended to expand our knowledge of the components involved in the pathogenesis of human allergic disease, with the general goal of identifying elements or processes that might be targeted for therapeutic intervention. Most specifically, this grant focuses on the role human basophils play in chronic allergic processes as IgE-bearing cells having remarkable ability to produce large quantities of IL-4 and IL-13 -the two most recognized Th2 cytokines at the core of the allergic diathesis. Both IL-4 and IL-13 are critical in initiating IgE synthesis in B cells and in differentiating naive T cells into Th2 cells capable of producing other cytokines associated with allergic inflammation. These cytokines also promote the selective trafficking of eosinophils, lymphocytes, and basophils into allergic lesions by up-regulating specific adhesion molecules on the endothelium. While seminal studies in the mouse model first suggested that mast cells produce these cytokine in response to IgE-mediated activation, these findings have not extended to humans. In contrast, we have demonstrated that basophils produce far more IL-4 and IL-13 in comparison to any other blood leukocyte. Recent studies suggest that this is also true for cells found in allergic lesions. The mechanisms involved in the release of IL-4 and IL-13 in basophils are both different from each other and from those controlling mediator release, suggesting that pharmacological control of their secretion will also differ. New findings suggest that IL-4 and IL-13 are also differentially regulated in basophils following exposure to ligands that bind specific members of the Toll-like receptor (TLR) family. In particular, we have found that TLR9, the receptor responsible for binding CpG-DNA, is expressed on basophils and that exposure to CpG-DNA results in an inhibition of IgE-mediated IL-4 and IL-13 secretion. This may provide one mechanism for the clinical efficacy seen with a novel CpG-DNA-like material (AIC) that is currently in clinical trials for ragweed immunotherapy. In contrast, the IL-13 secreted by basophils in response to IgE-independent stimuli is enhanced with other TLR/ligand interactions. Thus, these differential effects on basophil IL-4 and IL-13, mediated through TLR, may also help in delineating the mechanisms regulating cytokine production.